Parse YAML files and make references/links

Migrated issue

Reported by: jhodgdon

Drupal 8.x uses various YML files for configuration. Some of them include references to classes, functions, methods, etc.

It would be useful if:
- When displaying YML files, these would turn into links
- When displaying a class/function/method, it would show the YML file as a "string reference" to this class/function/method.

As an example, core/modules/user/user.routing.yml references the method '\Drupal\user\UserRouteController::register. Here's the current contents of this file:

user_register:
  pattern: '/user/register'
  defaults:
    _content: '\Drupal\user\UserRouteController::register'
  requirements:
    _access_user_register: 'TRUE'

So it would be good if '\Drupal\user\UserRouteController::register' turned into a link to that method, and if \Drupal\user\UserRouteController::register() had a back-link of some sort to this YML file.